Hypothetical diagram for kidney regeneration by different types of renal and extrarenal progenitors. CD24+CD133+ renal progenitors (red) are localized at the urinary pole and are in close contiguity with podocytes (green) at one extremity (the vascular stalk) and with tubular renal cells (yellow) at the other extremity. A transitional cell population (red/green) displays features of either renal progenitors (red) or podocytes (green) and localizes between the urinary pole and the vascular pole. At the vascular stalk of the glomerulus, the transitional cells are localized in close continuity with cells that lack progenitor markers, but exhibit the podocyte markers and the phenotypic features of differentiated podocytes (green). On the opposite side, at the urinary pole, transitional cells (red/yellow) with a mixed phenotype between tubular cells (yellow) and progenitor cells (red). The directions of differentiation is indicated by the arrows (modified from ).